/Engine/Source/Editor/SceneOutliner/Public/SceneOutlinerGutter.h
Process a mouse up message
virtual [FReply](API\Runtime\SlateCore\Input\FReply) OnMouseButtonUp ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & MyGeometry, const [FPointerEvent](API\Runtime\SlateCore\Input\FPointerEvent) & MouseEvent )